SiC Wafer Thinning via Laser-Induced Separation
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Solution Overview
Problem
The high Mohs hardness of SiC substrates leads to excessive wear of abrasive members during grinding, resulting in poor economy and inefficiency in wafer thinning processes compared to silicon substrates.
Innovation Solution
A wafer thinning method that uses a laser beam to form modified layers and cracks inside the SiC substrate without grinding the back side, allowing for the application of an external force to separate the wafer into thinner sections, reducing the thickness without abrasive wear, and subsequent minor grinding to flatten the back side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the back side of SiC wafer is ground by a grinding wheel having abrasive members, then the thickness of the wafer is reduced to a predetermined thickness, but the abrasive members wear in an amount of approximately 4 times to 5 times the grinding amount of the wafer, causing very poor economy
Solution Approach 1:
The patent replaces the mechanical grinding system with a laser-based system. A laser beam is focused inside the SiC wafer to form a modified layer at a predetermined depth from the back surface. This modified layer serves as a separation start point that allows the wafer to be cleaved into thin sections without requiring extensive mechanical grinding, thereby eliminating the excessive wear of abrasive members while achieving the desired thickness reduction.
Solution Approach 2:
The patent performs preliminary laser treatment to create a modified layer inside the wafer before the final thinning operation. By pre-forming this modified layer at the desired separation depth, the subsequent cleavage process becomes much more efficient and requires minimal additional material removal, avoiding the need for extensive grinding that would cause abrasive wear.
2Manufacturing precision
If the back side of SiC wafer is ground by a grinding wheel, then the wafer thickness is reduced, but the grinding process is time-consuming and inefficient compared to silicon substrate grinding
Solution Approach 1:
The patent substitutes the slow mechanical grinding process with a rapid laser-based modification and cleavage process. The laser can quickly create the modified layer at the desired depth throughout the wafer, and the subsequent cleavage along this pre-formed separation plane is much faster than grinding through the entire thickness, significantly improving productivity.
Solution Approach 2:
The patent changes the physical state and properties of the SiC wafer by using laser energy to create a modified layer with different structural characteristics. This modified layer has altered physical properties that facilitate easy cleavage, transforming the difficult-to-grind SiC material into a form that can be rapidly separated into thin sections.
3Loss of substance
If a laser beam is focused inside the SiC substrate to form a modified layer, then the wafer can be separated without extensive grinding, but the process requires precise control of focal point depth and positioning
Solution Approach 1:
The patent incorporates feedback mechanisms to monitor and control the laser beam focusing position and depth. By using feedback from detection systems that monitor the laser interaction with the SiC wafer, the system can automatically adjust the focal point depth and positioning to ensure consistent modified layer formation at the desired separation depth, managing the complexity through intelligent control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively reduces the thickness of SiC wafers without abrasive wear, achieving significant economic benefits by minimizing abrasive tool wear and allowing reuse of the separated wafers as substrates.
Implementation Method 1
a separation start point forming step of setting the focal point of a laser beam having a transmission wavelength to the SiC substrate inside the SiC substrate at a predetermined depth from the second surface
Implementation Method 2
applying the laser beam to the second surface as relatively moving the focal point and the SiC substrate to thereby form a modified layer parallel to the first surface inside the SiC substrate at the predetermined depth and also form cracks extending from the modified layer along the c-plane
Data Source
AI summary
Disclosed herein is a wafer thinning method for thinning a wafer formed from an SiC substrate having a first surface and a second surface opposite to the first surface. The wafer thinning method includes a separation start point forming step of applying the laser beam to the second surface as relatively moving the focal point and the SiC substrate to thereby form a modified layer parallel to the first surface and cracks inside the SiC substrate at the predetermined depth, thus forming a separation start point, and a wafer thinning step of applying an external force to the wafer, thereby separating the wafer into a first wafer having the first surface of the SiC substrate and a second wafer having the second surface of the SiC substrate at the separation start point.